Checkout dividers were originally simple bars of wood of square section, on which was commonly printed the name of the retail establishment. Because of its proximity to the point of payment, it was found to be an attractive location for certain kinds of advertisement and display.
In order that the entire divider need not be discarded after each promotional campaign, checkout dividers including a clear outer sleeve eventually became widespread. Printed matter could be inserted into these sleeves and changed as desired. In such dividers, the printed matter is commonly retained by grooves in the transparent sleeve and by plastic end caps at each end.
Lenticular imaging has its own distinct history. Illusionistic lenticular effects directed in part to advertising were described in U.S. Pat. No. 592,631 issued in 1897 to Hollander. In 1899, a lenticular stereoscopic system for photography and printing was described by John Jacobson in U.S. Pat. No. 624,042 and U.S. Pat. No. 624,043. Optically variable lenticular signage was more thoroughly detailed by Curwen in U.S. Pat. No. 1,475,430. It may be appreciated that the utility of lenticular effects in marketing and consumer-directed imaging has long been understood.
In current practice, lenticular images are prepared by digitally interlacing a set of source images. This data file is then used to direct the printing of a physical image. The image may be printed directly to the reverse of a lens sheet, or may be printed separately and applied. Intermediately, the color channels may be printed on the lens and an opaque backer material such as paper or polymer film applied in a separate step.
Variable images using an opaque parallax barrier parallel and in some ways predate lenticular imaging. In May 1896 Swiss engineer Auguste Berthier published a description of his work in which he combined a vertical line screen with interlaced images to make stereoscopic images that could be viewed without glasses.
U.S. Pat. No. 725,527 issued to Frederic Ives describes a similar arrangement. Beginning in 1904, Eugène-Pierre Estanave applied Berthier's strategy to animate images, and by 1910 was combining depth and animation in a single image. Current images using such selective occlusion are sometimes made by printing a fine dot pattern on both sides of a clear sheet, rather than by a strict lineation.
In the scientific understanding, a hologram is a complex form of diffraction grating produced by capturing or synthesizing a field of interfering wavefronts. This original or synthesized scene may be reconstructed by illuminating the holographic record with a suitable directional light source.
The term “hologram” is used more loosely in the graphic arts to describe any graphic material that carries an ornamental diffraction gating. Diffraction gratings produce color and intensity variation by the interference of light, rather than selective light absorbents such as pigments or dyes.
Interference color, also known as structural color, characteristically changes in its visual properties depending on the relative position of the observer, the material, and the source of illumination. Diffractive graphic materials are often modified with tinting in the form of topcoats or local spot color to provide a particular chromatic effect.
The use of such manufactured diffractive reliefs in ornamentation and predates the invention of classical holography by several decades. For example, in U.S. Pat. No. 551,769 John Jacobson describes the fabrication of a turned die for the reproduction of iridescent, ornamental diffraction gratings. Additional methods and designs using diffractive materials are taught by Porter in U.S. Pat. No. 734,134, U.S. Pat. No. 734,135, and U.S. Pat. No. 734,361, by Doner in U.S. Pat. No. 1,354,471, and by Sylvester et al. in U.S. Pat. No. 2,875,543.
A third class of optically variable structured material employs gratings coarser than those needed to chromatically decompose light, yet still sufficient to impart a selectively directional effect. These reliefs may be combined with conscientiously applied transparent colorants to produce color effects in the absence of diffraction. Representative examples of this class of material are described in U.S. Pat. No. 1,996,539 to Dufay and UK 438236 to Weil.
Optically variable graphic materials can be made using refraction, occlusion, diffraction, or reflection, or any combination of these principles. These principles can be called upon to impart an image that conveys a variation with the relative position of the observer. These principle can be broadly employed to produce a range of effects, including animations, color shifts, alternating messages, or the impression of stereoscopic depth.
Visually variable images which are actuated by electromechanical means are also widely represented in the record. One standard method of eliciting an optical effect is to induce a relative motion between image and lens. Comparatively few lenticular products relate to passive motion or motion induced by an external source.